1. Field of the Invention
The present invention relates to a method of folding a bag for an air bag apparatus which is accommodated in a folded state in an apparatus main body, and is deployed and inflated toward a vehicle occupant as an ejected gas flows into the bag on impact of a predetermined high load to a frontal portion of a vehicle, as well as an air bag apparatus incorporating the bag.
2. Description of the Related Art
Conventionally, by devising methods for folding bags of air bag apparatuses, attempts have been made to improve the deployment performance of the bags on impact of a predetermined high load to a frontal portion of a vehicle so as to improve the performance of occupant protection. As an example of disclosure of this type of bag folding method, it is possible to cite Japanese Patent Application Laid-Open (JP-A) 7-277125, and a brief description will be given hereinunder of the bag folding method disclosed in this publication.
FIGS. 8A to 8K show the procedure of folding a bag 250 of an air bag apparatus for a driver seat. The bag 250 is formed by sewing together peripheral portions of two pieces of base cloth which are respectively cut into circular shapes.
First, as shown in FIG. 8A, the bag 250 is set in a planarly laid-out state. Then, as shown in FIG. 8B, a lower portion 254 of the bag is folded at a folding line 252 which is parallel with a center line X. Then, as shown in FIG. 8C, a distal end portion 258 of the lower portion 254 of the bag is folded back to the opposite side at a folding line 256 which is parallel with the center line X. Then, as shown in FIG. 8D, the distal end side portion of the lower portion 254 of the bag is folded in the same direction at a folding line 260 which is parallel with the center line X. Further, the distal end side portion of the lower portion 254 of the bag is folded in the same direction at a folding line 261 on the center line X. As a result, a lower foldedup portion 262 is formed as shown in FIG. 8E. Subsequently, an upper portion 264 of the bag is also folded in a procedure similar to the one described above. Consequently, an upper folded-up portion 266 is formed in such a manner as to be symmetrical with the lower folded-up portion 262 with respect to the line X.
Next, as shown in FIG. 8G, a right-hand portion 270 of the bag is folded at a folding line 268 which is parallel with a center line Y. Then, as shown in FIG. 8H, a distal end portion 274 of the right-hand portion 270 of the bag is folded back at a folding line 272 which is parallel with the center line Y. Then, as shown in FIG. 8I, the distal end side portion of the right-hand portion 270 of the bag is folded in the same direction at a folding line 276 which is parallel with the center line Y. Then, as shown in FIG. 8J, the distal end side portion of the right-hand portion 270 of the bag is further folded in the same direction at a folding line 278 which is parallel with the center line Y. As a result, a right folded-up portion 280 is formed. Subsequently, a left-hand portion 282 of the bag is also folded in a procedure similar to the one described above. Consequently, a left folded-up portion 284 is formed in such a manner as to be symmetrical with the right folded-up portion 280 with respect to the line Y.
Namely, with the above-described folding method, the bag 250 is first folded in the vertical direction by using the center line X as a reference to form the lower folded-up portion 262 and the upper folded-up portion 266 which are belt-shaped. Then, the bag 250 is folded in the horizontal direction by using the center line Y as a reference to form the right folded-up portion 280 and the left folded-up portion 284 which are rectangular in a plan view. At this time, in both procedures of forming the folded-up portions, the bag 250 is folded in the same direction in the second and subsequent foldings. As a result, when the bag 250 is inflated, the right folded-up portion 280 and the left folded-up portion 284 are first unfolded in the horizontal direction, the lower folded-up portion 262 and the upper folded-up portion 266 are then unfolded in the vertical direction, and the overall bag 250 is subsequently inflated toward the occupant. Accordingly, the arrangement provided is such that the bag 250 is unfolded in the horizontal direction and then in the vertical direction in an early stage of inflation.
Conceivably, such a method of folding the bag 250 and, hence, the manner of deployment of the bag 250 in the early stage of inflation are able to obtain their due advantages in light of the performance of occupant protection.
However, in accordance with the above-described arrangement, since the right folded-up portion 280 and the left folded-up portion 284 are first unfolded in the horizontal direction, and the lower folded-up portion 262 and the upper folded-up portion 266 are then unfolded in the vertical direction, one unfolding (unfolding in the vertical direction) is dependent on the other unfolding (unfolding in the horizontal direction). If such dependence can be canceled and the bag can be unfolded in both the vertical direction and the horizontal direction at the same time in the early stage of inflation, it is thought that an optimum state of bag deployment can be obtained, making it possible to further improve the performance of occupant protection.